GRL

The electron density of the Martian ionosphere is modulated by solar wind forcing and crustal magnetic fields. Sounding observations from the orbital Shallow Radar (SHARAD) map the ionospheric total electron content (TEC) at a spatial resolution of ∼35 km. Averaging over a 250-km diameter window from data collected weeks to years apart yields the first map of long-term stable dayside martian TEC features. An extensive region of suppressed TEC in the southern highlands correlates with strong radial magnetic fields, but in other areas no simple correlation is observed. The TEC maps do follow the outlines of exposed Noachian crust and patches of magnetization in Tharsis not reset by volcanic activity. SHARAD TEC mapping may capture magnetic field strength at an intermediate height between the surface and the altitudes of orbital measurements underlying spherical harmonic models. Existing and future data will allow SHARAD TEC mapping to ∼100 km spatial resolution.

Polythermal glaciers can trap considerable volumes of liquid water with the potential to generate devastating outburst floods. This study aims to identify water-filled subglacial reservoirs from ambient seismic noise collected by moderate-cost surveys. The horizontal-to-vertical spectral ratio technique is highly sensitive to impedance contrasts at interfaces, thus commonly used to estimate glacier thickness. Here, we focus on the inverse ratio, that is, the V/H spectral ratio (VHSR), whose high values indicate a low impedance volume beneath the surface, suggesting subglacial cavities. We analyze VHSR peaks from a seismic array of 60 nodes installed on the Tête-Rousse Glacier (Mont Blanc massif, French Alps); data were gathered over 15 days. Mapping the VHSR amplitude over the free surface reveals the main cavity locations and the basal areas affected by melting within the glacier. Results obtained in the field are supported by a conceptual model based on 3D finite-element simulations.

The stress redistribution from an earthquake can produce localized measurable rotations of the principal stress axes if the absolute level of differential stress in the crust is on the order of the earthquake stress drop. Two simple analytic solutions have been developed to estimate the differential stress from an observed stress rotation. However, each has assumptions that may not be accurate near Earth's free surface. I model synthetic earthquakes in an elastic half-space, and show that the assumptions of the methods are accurate for strike-slip earthquakes, and for deep dip-slip earthquakes. However, they are incorrect for shallow dip-slip earthquakes. I introduce a free surface correction for one of the methods for dip-slip earthquakes. I revise an analysis of stress rotations due to great subduction zone earthquakes, including this correction. The results support the original conclusion of near complete stress drop for many shallow subduction zone earthquakes.

Remote sensing detection of autumn phenology is challenging and highly uncertain, as exemplified by the observed divergence in autumn phenology extracted from different proxies. Here, we compared the autumn phenology derived from Solar-Induced chlorophyll Fluorescence (SIF), Chlorophyll/Carotenoid Index (CCI), Enhanced Vegetation Index (EVI), and Normalized Difference Vegetation Index (NDVI) over deciduous forest sites. We observed a clear temporal sequence in the derived autumn phenology from various proxies: SIF < CCI < EVI < NDVI. Comparison with field measurements supported that SIF, EVI, and NDVI can successfully capture the attenuation of photosynthetic activity, leaf coloration, and leaf fall, respectively. The sequence among the autumn phenology derived from those proxies was also consistent with their responses to climate cues, where SIF had the highest partial correlation coefficient to solar radiation in autumn, followed by CCI, EVI, and NDVI, while NDVI was more correlated with temperature, followed by EVI, CCI, and SIF.

Coral reef islands are amongst the most vulnerable environments to sea-level rise (SLR). Recent physical and numerical modeling studies have demonstrated that overwash processes may enable reef islands to keep up with SLR through island accretion. Sediment supply to these islands from the surrounding reef system is critical in understanding their morphodynamic adjustments, but is poorly constrained due to insufficient knowledge about sediment delivery rates. This paper provides the first estimation of sediment delivery rates to coral reef islands. Analysis of topographic and geochronological data from 28 coral reef islands indicates an average rate of sediment delivery of c. 0.1 m3 m−1 yr−1, but with substantial inter-island variability. Comparison with carbonate sediment production rates from census-based studies suggests that this represents one quarter of the amount of sediment produced on the reef platform. Results of this study are useful in future modeling studies for predicting morphodynamic adjustments of coral reef islands to SLR.

Sea ice topography information can be obtained from altimetry but these data are spatially and temporally limited compared to recent synthetic aperture radar (SAR) missions such as the RADARSAT Constellation Mission (RCM). We analyze the relationship between sea ice roughness and height obtained from three Ice, Cloud, and Land Elevation Satellite (ICESat)-2 tracks on two dates in March 2022, with RCM backscatter from 17 images in the McClintock Channel, Canadian Arctic. We analyze how this relationship varies with ice type, polarization, and incidence angle. We find particularly notable relationships between sea ice roughness and horizontal-transmit/vertical-receive backscatter for first-year ice, and sea ice height and backscatter for multi-year ice. We develop a preliminary model for winter sea ice roughness retrieval using RCM. In comparison with independent ICESat-2 data in our study region, we find the model performs effectively at estimating a roughness distribution and key roughness statistics, and characterizes spatial variations in roughness at a sub-kilometer scale.

Earthquake swarms are most commonly composed of small-magnitude earthquakes. However, a recent study by Yoshida, Uchida, et al. (2023, https://doi.org/10.1029/2023GL106023) analyzed a swarm beneath the Noto Peninsula in Japan that, after more than two years of moderate-magnitude seismicity, triggered the moment magnitude (M w ) 6.2 Suzu mainshock in May 2023. Based on high-precision earthquake locations and a slip inversion of the mainshock, these authors found that the M w 6.2 Suzu earthquake occurred on the updip extension of a fault that was active during the swarm, likely driven by increased fluid pressure. After publication of that paper, a much larger and more destructive M w 7.5 event occurred nearby on 1 January 2024. These events underscore the potential for swarms to be precursors to large, damaging earthquakes. Forecasting the eventual evolution of swarms is currently very challenging but could be aided in the future by new observations and models.

In mixed-phase cumulus clouds, droplets and ice crystals are inhomogeneously distributed, such spatial inhomogeneity can be enhanced by inhomogeneous entrainment as it can strengthen the particle clustering, which may further influence the phase partitioning and interactions among hydrometeors. However, the scale of particle clustering induced by inhomogeneous entrainment is not well known. Utilizing high-resolution in-situ aircraft measurements in mixed-phase cumulus clouds, this study shows due to inhomogeneous entrainment-mixing, the cluster scales of droplets and ice crystals decrease by approximately 10 m from the cloud center to the edge. Changes in the clustering are correlated with the intensity of entrainment-mixing. Clouds that are significantly affected by entrainment exhibit stronger enhancement of particle clustering and a more noticeable reduction in cluster scale. The findings from this study improve our understanding of the scale of particle clustering induced by entrainment-mixing, and are potentially helpful in evaluating models.

Coastal protection is of paramount importance because erosion and flooding affect millions of people living along the coast and can largely influence countries' economy. The implementation of nature-based solutions for coastal protection, such as sand engines, has become more popular due to these interventions' adaptability to climate change. This study explores synergies between Artificial Intelligence (AI) and hydro-morphodynamic models for the creation of efficient decision-making tools for the choice of optimal sand engines configurations. Specifically, we investigate the use of long-short-term memory (LSTM) models as predictive tools for the morphological evolution of sand engines. We developed different LSTM models to predict time series of bathymetric changes across the sand engine as well as the time-decline in the sand engine volume as a function of external forces and intervention size. Finally, a MATLAB framework was developed to return LSTM model results based on users' inputs about sand engine size and external forcings.

In recent decades, the ocean CO2 uptake has increased in response to rising atmospheric CO2. Yet, physical climate change also affects the ocean CO2 uptake, but magnitude and driving processes are poorly understood. Using a global ocean biogeochemistry model, we find that without climate change, the mean carbon uptake 2000–2019 would have been 13% higher and the trend 1958–2019 would have been 27% higher. Changes in wind are the dominant driver of the climate effect on CO2 uptake as they affect advective carbon transport and mixing, but the effect of warming increases over time. Roughly half of the globally integrated wind-driven trend stems from the subpolar Southern Ocean and polar oceans in both hemispheres. Warming reduces the solubility of CO2 and acts rather homogeneously over the world oceans. However, the warming effect on pCO2 is dampened by limited exchange of surface and deep waters.

Although carbonates are the primary form of carbon subducted into the mantle, their fate during recycling is debated. Here we report the first coupled high-precision Zn and Mo isotope data for Cenozoic intraplate basalts from western China. The exceptionally high δ66Zn values (+0.39 to +0.50‰) of these lavas require involvement of recycled carbonates in the mantle source. Variable δ98Mo compositions (−0.39 to +0.27‰) are positively correlated with Mo/Ce, best interpreted as mixing between isotopically light Mo from dehydrated oceanic crust and heavy Mo from recycled carbonates, which is also supported by positive coupling between δ66Zn and δ98Mo. Modeling reveals that involvement of ≤5% carbonate-bearing oceanic crust fully resolves the observed δ66Zn–δ98Mo mantle heterogeneity probed by intracontinental basalts. Our study demonstrates that combined δ66Zn–δ98Mo data sets for mantle-derived magmas can track recycled surficial carbonates in Earth's interior, providing a powerful geochemical tool for deep carbon science.

Kangerlussuaq Glacier (KG) is a major contributor to central-eastern Greenland mass loss, but existing estimates of its mass balance over the last century are inconsistent, and specific drivers of change remain poorly understood. We present a novel approach that combines numerical modeling and a 1933–2021 climate forcing to reconstruct its mass balance over the past century. The model's final state aligns remarkably well with present-day observations. The model reveals a total ice mass loss of 285 Gt over the past century, equivalent to 0.68 mm global sea level rise, 51% of which occurred since 2003 alone. Dynamic thinning from ice front retreat is responsible for 88% of mass change since 1933, with short-term ice front variations having minimal impact on centennial mass loss. Compared to earlier studies, our findings suggest that KG lost 59% (or 301 Gt) less mass over the century than previously thought.

Using observations and Atlantic forced coupled model simulations, we show evidence for an asymmetry in the link between beginning of year tropical Atlantic sea surface temperature anomalies (SSTAs) and end of the year El Niño-Southern Oscillation events. We find a greater tendency for warm Atlantic SSTAs to lead to a La Niña than for cold anomalies to lead to El Niño. The model experiments showed that the Atlantic had a greater chance to force the tropical Pacific if the Pacific was initially in a neutral state. In the model, a warm Atlantic from March–May was able to produce an atmospheric response leading to easterly wind anomalies in the western Pacific. This in turn induces a subsurface oceanic response, leading to La Niña at the end of the year. The atmospheric response does not occur for a cold Atlantic, leading to no impacts in the Pacific.

The D/H ratio in water on Mars, Rwater, is 4–6× the Earth ratio, signifying past water loss to space. Recently, measurements have revealed high values of the D/H ratio in hydrogen, Ratomic, in the thermosphere during southern summer. Here, we use a photochemical model to explore the potential drivers of Ratomic, testing three: thermospheric temperatures, excess mesospheric water, and changing insolation. We find that Ratomic can achieve values between 15× the Earth ratio (due to water) and 23× the Earth ratio (due to temperature). The effects arise because H escape is diffusion-limited, while D escape is energy-limited. Our results underscore how Ratomic reflects mesospheric dynamics, and the need for concurrent measurements of mesospheric water, thermospheric temperatures, and Ratomic to understand seasonal changes in the martian water cycle and atmospheric loss.

As sea ice disappears, the emergence of open ocean deep convection in the Arctic, which would enhance ice loss, has been suggested. Here, using 36 state-of-the-art climate models and up to 50 ensemble members per model, we show that Arctic deep convection is rare under the strongest warming scenario. Only five models have convection by 2100, while 11 have had convection by the middle of the run. For all, the deepest mixed layers are in the eastern Eurasian basin. When that region undergoes a salinification and increasing wind speeds, the models convect; yet most models are freshening. The models that do not convect have the strongest halocline and most stable sea ice, but those that lose their ice earliest -because of their strongly warming Atlantic Water- do not have a persistent deep convection: it shuts down mid-century. Halocline and Atlantic Water changes urgently need to be better constrained in models.

Attaining skillful decadal predictions for the western North Pacific tropical cyclone (TC) emerges as a formidable challenge, mainly stemming from the limited prediction skills of Pacific Decadal Variability (PDV) within the state-of-the-art models. Assessing sixth Coupled Model Intercomparison Project models' retrospective predictions finds that the predictability of PDV transcends the expectations set by raw forecasts featured by constrained temporal skills and low signal-to-noise ratio. Employing a refined approach, we selectively identify the models that capture the diverse phases of PDV and subsequently adjust their variances. This tailored approach yields a compelling concordance between the predicted PDV and observation in phases and variances. Anchored in the heightened prediction skill of PDV, we establish a sophisticated statistical model adept at predicting the latitude of TC's lifetime maximum intensity (LMI). The near-term prediction indicates a sustained poleward migration of LMI latitude by 1.53° during 2020–2027, increasing subtropical East Asia's TC-related disaster vulnerability in the coming decade.

Sulfur-based stratospheric aerosol intervention (SAI) can cool the climate, but also heats the tropical lower stratosphere if done with injections at low latitudes. We explore the role of this heating in the climate response to SAI, by using mechanistic experiments that remove the effects of longwave absorption of sulfate aerosols above the tropopause. If longwave absorption by stratospheric aerosols is disabled, the heating of the tropical tropopause and most of the related side effects are strongly alleviated and the cooling per Tg-S injected is 40% bigger. Such side-effects include the poleward expansion of eddy-driven jets, acceleration of the stratospheric residual circulation, and delay of Antarctic ozone recovery. Our results add to other recent findings on SAI side effects and demonstrate that SAI scenarios with low-latitude injections of absorptive materials may result in atmospheric effects and regional climate changes that are comparable to those produced by the CO2 warming signal.

Arctic temperature is one of the most uncertain aspects of mid-Holocene (MH) climate change modeling, usually attributed to the different responses of different models to external forcing. However, in this study, we find that significant discrepancies (i.e., the noise is close to the signal in term of climate change) in the MH Arctic temperature changes can occur within the same model and for identical external forcing due to initial ocean condition perturbations. It is shown that initial ocean perturbations can affect the surface energy budget change through the uncertain cloud effect on shortwave radiation in boreal summer. The resulted uncertain change in summer surface heat flux alters the subsequent autumn and winter sea ice and contributes to significant differences in Arctic temperature via sea ice-albedo feedback. This study suggests that internal uncertainty of an individual model is a non-negligible source of overall uncertainty in simulating the MH Arctic temperature change.

Multidecadal sea surface temperature (SST) variations in the tropical western Pacific (TWP) have been attributed to nonlinear external forcing and remote influences from the Atlantic Multidecadal Variability (AMV). However, the AMV resulted from both internal variability (IV) and external forcing. Thus, the origins of the TWP SST variations are not well understood. By analyzing observations and model simulations, we show that more than half of the decadal to multidecadal SST variations in TWP during 1920–2020 resulted from external forcing with the forced component correlated with AMV, while the internal component is unrelated to AMV. Furthermore, about 43%–49% of the forced AMV-like SST variations in TWP result from remote influences of the forced AMV in the Atlantic via atmospheric teleconnection over the North Pacific, with the rest from other remote or local processes.

Mesoscale and submesoscale processes have crucial impacts on ocean biogeochemistry, importantly enhancing the primary production in nutrient-deficient ocean regions. Yet, the intricate biophysical interplay still holds mysteries. Using targeted high-resolution in situ observations in the South China Sea, we reveal that isopycnal submesoscale stirring serves as the primary driver of vertical nutrient transport to sustain the dome-shaped subsurface chlorophyll maximum (SCM) within a long-lived cyclonic mesoscale eddy. Density surface doming at the eddy core increased light exposure for phytoplankton production, while along-isopycnal submesoscale stirring disrupted the mesoscale coherence and drove significant vertical exchange of tracers. These physical processes play a crucial role in maintaining the elevated phytoplankton biomass in the eddy core. Our findings shed light on the universal mechanism of how mesoscale and submesoscale coupling enhances primary production in ocean cyclonic eddies, highlighting the pivotal role of submesoscale stirring in structuring marine ecosystems.